COVID-19: Pneumonia: management of respiratory failure (Guidelines)

The pathophysiology of respiratory failure in patients with COVID-19 pneumonia appears to be collapse of distal airways. Ventilation-perfusion (V/Q) mismatch results in hypoxia. This is important because when appropriate CPAP or invasive ventilation can re-recruit collapsed alveoli. In addition it is important to avoid any treatments that might worsen V/Q mismatch. Salbutamol and other beta-agonists are known to have this effect, so should be avoided unless there is known or suspected asthma or COPD.

It should be noted that these guidelines relate to patients with COVID-19 pneumonia, and the management of an exacerbation of COPD should follow existing guidance, except with the addition of use of AGP PPE if NIV is being used.

CPAP and non-invasive ventilation (NIV) are  aerosol generating procedures (AGP) so can only be used in side rooms or cohort areas with all staff in that area wearing full AGP PPE

During resuscitation (if required) an oxygen saturation of 94-98% should be achieved, using nasal cannulae, a standard oxygen mask or a non-rebreathing reservoir mask (NRBM). Nasal cannulae are the preferred choice for low oxygen flow rates. The initial choice of device should be determined by the severity of hypoxia and equipment availability.  The associated flow chart gives the approximate percentage of oxygen that these devices deliver at different flow rates. Non-rebreathing masks, when used, should always run at on oxygen flowmeter setting of 15L/min. Lower flows when using this mask may significantly increase the work of breathing. During treatment an oxygen saturation of 94-98% should be maintained. Higher oxygen saturations can have a number of important deleterious effects. It is advised that a standard (non-Venturi) oxygen mask is used, because a Venturi mask results in higher total gas flows, and therefore is may result in greater dispersal of respiratory droplets.  A Venturi device also uses 15 litres/min for 60%, and a simple face mask uses less to achieve an equivalent FiO₂.The oxygen flow rate should be adjusted as suggested on the flow chart to target the required oxygen saturation. It should be noted that a lower oxygen saturation may need to be targeted if concerns arise regarding supplies, and individual units will need to determine if it is necessary to temporarily set lower targets of 92-94%, or 90-92% in the context of a Super-Surge or Code Red scenario.  Patients with known severe COPD or chronic type 2 respiratory failure should have a lower target saturation (88-92%). All patients requiring oxygen within 24 hours of admission or those requiring 40% oxygen, and those with type 2 respiratory failure should have continuous pulse oximetry monitoring.

If the above intervention does not result in adequate oxygen saturation, or if the patient is otherwise deteriorating a decision will need to be made regarding escalation. Clinicians should focus on current clinical needs and should not treat patients differently because of anticipated future pressures[2]. In making decisions they should work collectively with each other and with their organisations, and take into account all possible routes of escalation and mutual aid. Clearly a frail patient in their 80’s with multiple morbidities should not have their treatment escalated, whereas a patient who is 65 and previously fit and well should be considered for invasive ventilation. It is the large group in the middle about which there is more uncertainty.  NICE guidelines advise calculation of clinical frailty score (CFS) which may form part of the decision making process. A score of 5 or more would be a relative contraindication for ITU. The decision will depend on factors that are likely to include age, pre-existing morbidities, and CFS. The Intensive Care Society has produced a helpful document² to facilitate decision making and is essential reading. Where it is felt that there is a rapid deterioration in a patient’s condition they should be discussed with the on call ICU consultant (speed dial 3030) for Raigmore Hospital, or using agreed local arrangements for rural general hospitals.

While decisions are being made regarding escalation it would be appropriate to initiate oxygen via NRBM. In a patient who is deteriorating rapidly and is appropriate for escalation to invasive ventilation it may not be desirable for them to receive NIV which might delay intubation.

There will be patients in whom non-invasive forms of respiratory support may be sufficiently successful to avoid intubation. It should be remembered, though, that COVID-19 pneumonia is often a prolonged illness and non-invasive respiratory support may need to be continued for some time, and very prolonged CPAP may not be tolerated.

If patients are already on 40% oxygen and show further deterioration then they should be considered for CPAP. Patients requiring advanced respiratory support (CPAP or HFNO if CPAP is not tolerated) will be located in the Respiratory Support Unit. The ITU team will assess patients with a view to admission if they need advanced respiratory support and they also have other organ dysfunction and are suitable for level 2 care. The ITU team will also assess patients with a view to admission who are deteriorating despite advanced respiratory support including requiring more than 60% oxygen if they are considered suitable for level 3 care.

HFNO and CPAP should not be used in the RGH. Early transfer should be the priority.

High flow Nasal Oxygen (HFNO) can deliver a very high FiO₂.  For COVID-19 there is no evidence that it offers any prognostic advantages over conventional oxygen therapy. In view of this NICE guidelines advice that it should only be used for meal breaks from CPAP, as part of a weaning strategy from CPAP, or to provide humidification.

Continuous positive airway pressure (CPAP) has been found to be an effective intervention for some patients. There are several key points:

For this therapy to be used safely, NHS Highland must work towards achieving the nationally agreed standards for establishing respiratory support units both in terms of infrastructure, monitoring and safe staffing levels³.

1. It is aerosol generating (as indicated above).
2. The starting settings for CPAP should be 60% oxygen and a CPAP pressure of 5 to 7cm H₂0 increasing to 10cm H₂0 as tolerated. Experience in Italy was that relatively high pressures are required (Median PEEP 14cm H₂0). This may not be tolerated by all patients. Please be aware that high pressures may reduce venous return and thereby cardiac output: watch out for haemodynamic compromise and escalate PEEP gradually.
3. It is possibly best to deliver CPAP using a mask system using the Trilogy ventilator, or alternatively by using the hood system.
4. If a mask is used there must always be appropriate filters in place. Pre-prepared circuits have been provided to facilitate this. A non-vented mask, and vented tubing should always be used.
5. A trial of CPAP is reasonable for patients who do not need to be intubated immediately. If a patient deteriorates despite the use of 40% oxygen then they should be considered for CPAP therapy. The threshold for intubation and ventilation should be failure to improve, and the inability to have breaks to eat and drink. HFNO can be used for CPAP breaks.
6. It should only be used at Raigmore Hospital.

Non-Invasive ventilation (NIV) is an option for some patients, in the form of bi-level respiratory support. This may be the case in patients with existing airway disease with associated type 2 respiratory failure. There are three important points:

1. It is an AGP and should therefore be limited to areas in which staff are wearing AGP-PPE
2. When starting NIV the mask should be put in place before starting NIV, and the NIV should be stopped before the mask is removed.
3. A non vented mask, and vented tubing must always be used. An appropriate pre-prepared circuit with filters in place should always be used.

[1] BTS/ICS Guidance: Respiratory care in patients with Acute Hypoxaemic Respiratory Failure associated with COVID-19 December 2020 (available on British Thoracic Society Website)

[2] Clinical Guidance: Assessing whether COVID-19 patients will benefit from critical care, and an objective approach to capacity challenges (August 2020)

³ BTS/ICS Respiratory support units: Guidance on development and implementation. June 2021 (available on British Thoracic Society Website)